Continuous production and stabilization of nitrates of cellulose or nitrates of other alcohols like starch



Sept. 4, 1945. E. BERL 2,334,415

CONTINUOUS PRODUCTION AND STABILIZATION 0F NITRATES OF CELLULOSE ORNITRATES OF OTHER ALCOHOLS LIKE STARCH Filed March 27, 1941 Jbll/e): t lquor:

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IN V EN TOR.

ATTORNEY Patented Sept. 4,

con'rmuous PRODU ZATION OF NITRA ON AND ST S 0F CELLULOSE OB NI'IRATESOF OTHER ALCOHOLS LIKE STABCH Ernst Berl, Pittsburgh, Pa.

Application March 27, 1941, Serial No. 385,580

13 Claims. (Cl. 260-220) The continuous production and stabilization ofcellulose nitrates or nitrates of other alcohols like starch has beentried rather often but up to now without any industrial success. Thediillculties were that the speed of nitration was not high enough sothat during a rather short treatment of the material to be nitrated withthe nitrating acid it was not possible to introduce the necessary amountoi nitrogen into the molecule of the alcohol. Certain constructions gavenitrates which represented mixtures of nitrates with higher and lowernitrogen content and, therefore, of low industrial value. p The removalof the, spent acid 1 from the nitrated material and the furtherstabilization took a long time so that the goalquick nitration-andquick, complete elimination oi, the absorbed and adhering spent acid,and

quick stabilization-has not been realized up to now.

It has been found that the following described way represents a solutionof this problem. In the same machines in which cellophane is produced,or in other appropriate constructions, dried, thin sheets of permeablepaper made from cellulose practically free of foreign substances, likelignin, lower carbohydrates, oils, fats, and ash components, and with alow content of beta and gamma cellulose are introduced in a mixed acidwhich is composed of nitric acid, phosphoric acid, and a few percent(440%) of free phosphoric acid anhydride. One can at the same timeeasily introduce several sheets of cellulosic material which are keptseparated by rods or any other simple arrangement. The relative movementof mixed acid oi this kind toward the continuously introduced sheets ofthiscellulose paper weighing not more than 30 or 40 grams per sq. meter,but preferably only about 20 grams per sq. meter, can be made in countercurrent or in parallel stream.

The very astonishing fact has been found that then the nitration underformation of a highly nitrated material with about 13.95% of nitrogencan be eiiected in only a few seconds or minutes. Another unexpectedeffect is that the nitric acid content of this mixed acid which inthefresh acid may be 50 to 60% can be reduced to a few tenths of a percentin the spent acid during this nitration. No appreciable attack of theformed highly nitrated cellulose through the resulting, nearlynitric-acid-iree, spent acid can be observed. The nitration can becan'ied out at roomtemperature or somewhat elevated temperature (50-70C.)

without any appreciable degradation of the cellulose molecule. Thenitration can be carried out:

also at lower temperatures than room temperature. Then the solubility ofthe resulting cellulose nitrate is aiiected and partly or whollyinsoluble cellulose nitrates can be obtained, in spite of the highdegree of nitration. This change in the solubility characteristics maybe of importance for the production of certain smokeless powders.

The same results can be obtained with a mixture of water-free nitricacid and glacial acetic acid which may contain some acetic anhydride.This mixture will contain to of an anhydrous nitric acid. It can be usedunder exactly the same conditions as the mixed acid composed of nitricacid and phosphoric acid and phosphoric acid anhydride at normal,slightly elevated, or at lower temperature.

One can use also mixtures of these mixed acids; in other words, mixedacid composed of nitric acid, phosphoric acid, glacial acetic acid andphosphoric acid anhydride. 7

The reason for the high speed of nitration is the swelling of celluloseand cellulose nitrate in phosphoric acid and iii-glacial acetic acid.This swelling enlarges the internal surface of the material anddiffusion and backdiiiusion of acids are facilitated.

The resulting nitrates contain one-half or more percent'of boundnitrogen (13.8.-14.0% N) more than can be obtained with sulfuric acidcontaining mixed acids (maximum nitrogen content after stabilization13.3% N). The spent acid can be pressed out by passing the materialthrough rollers so that the nitrated material contains relatively littleadheringfspent acid. can be removed very quickly by washing first withcold and then with warm water. Again by passage through rollers, theadhering liquid can be pressed out. I

e The strengthening of spent acid resulting from a treatment ofcellulose or other alcohols with phosphoric acid containing mixed acidcan be. carried out with strong nitric acid and the addi- 'tion ofeither P205 or meta phosphoric acid (HPOa) so that the original strengthwill result. Using nitrating mixtures of nitric acid and glacial aceticacid, the addition of water-free nitric acid, and the addition of Iacetic anhydride or ketene brings the spent acid back to the compositionof the original nitrating mixture.

It is very remarkable that the nitration process of cellulose or otheralcohols with mixed acid composed either of nitric acid, phosphoric acidand free P205 or of nitric acid, glacial acetic acid with or withoutadditional amounts of acetic anquickly under formation of oxalic acidand other 10 organic acids on one hand, and nitrososulphuric acid on theother hand. Therefore, spent acids after several repetitions ofnitrations result which are very impure and which give rise to a strongdecomposition during subsequent nitrations. Theorganic part is thenburned to carbon dioxide and the nitric acid is transformed intodangerous lower nitric oxides. These disadvantages are not observed withthese aforementioned mixtures containing phosphoric acid, or aceticacid. or both. This also simplifies considerably the whole process.

It is very remarkable that the stabilization can be carried out veryquickly in a very short time (fractions of or several minutes) withpecial stabilization methods because phosphoric acid or glacial aceticacid containing mixed acids do not form mixed esters of cellulose of thetype of cellulose sulfato nitrates which results from the nitration ofcellulose with sulfuric acid containing mixed acids and which arerelatively difiicult to decompose. A treatment with swelling agents likealcohol or with mixtures of swelling and nonswelling agents like alcoholand benzene which are kept at or near the boiling point is sufilcient toremove quickly those substances which cause the instability. Thosesubstances are mostly nitrates of lower carbohydrates which are presentin the cellulosic material before nitration. -A.fter repeated treatmentwith hot alcohol, or hot alcohol-hydrocarbon mixtures, oralcohol-chlorinated hydrocarbon mixtures, and following drying ifnecessary, one has obtained in a continuous process which lasts only afew minutes completely stable cellulose nitrates which contain up to13.95% of bound nitrogen. In most cases the alcohol-containing material,after stabilization can be used without the complete removal of alcoholfor the production of smokeless powder, plastic masses, etc. The excessof alcohol or alcohol-containing liquid may be eliminated by pressingout or by centrifuging. Through this special kind of nitration andstabilization, the resulting nitrates show a stability which is higherthan the stability of the best stabilized cellulose nitrate's made withacids containing sulfuric acid. 'The production of the latter-mentionedstabilized materials takes more than 100 times longer than the processesof nitration and stabilization described in this specification.

It is remarkable that nitrates with very high stability can be'obtainedwithout having those nitrated fibers pulped. The classical stabilizationby boiling with .diluted acids and diluted alkalis does not givesatisfactory results with long fibers. They have to be cut into shortpieces by pulping which costs time and power. These expenditures can beavoided by the use of a stabilization process whereby swelling. but notdissolving, agents remove mixed esters like cellulose nitratosulfates,furthermore, strongly adsorbed mineral acids and nitrates and nitritesof lower carbohydrates, for example. dextrose nitrates.

assure the same machines which are used now for the production ofCellophane, or films, or foils can be used with. relatively smallchanges for the continuous production of cellulose nitrates in. form ofthose nitrated and stabilized sheets. For other alcohols, for example,sugar, starch. slic- ,erine, glycol, or pentaerythrite, etc., otherapprophoric acid which may contain iron and aluminum salts. Comparativeexperiments have shown that filter cloth made with an acid mixturecomposed of sulfuric acid, nitric acid and water was destroyed by atreatment with a 70% phosphoric acid at 70 0. within 12 hours, and thatfilter cloth made with a mixture of phosphoric acid, nitric acid andPzOs, or with glacial acetic acid and water-free nitric acid, showed thesame attack after '1 to 14 days under the same conditions of corrosion.These tissues nitrated according to the prescription of this patentspecification can be used also with the greatest success as powder bagsfor military purposes.

The accompanying drawing shows an apparatus for carrying out thecontinuous process as above described; the scope of the invention,however, is not limited to the particular apparatus shown.

Figure 1 shows a longitudinal section, and

Figure 2 shows a top view of the apparatus.

The apparatus consists of along container divided in compartments forthe nitrated bath, for a washing bath (cold or hot) and for astabilization bath with swelling agents. Transverse rollera are arrangednear the bottom and near the top of the compartments for continuallyconducting through the container a continuous sheet of cellulosematerial. These rollers are suitably arranged to present a large surfaceof the sheet to the respective baths. The compartments may also beequipped with baiiies. Inlets and outlets are provided in eachcompartment for admitting and withdrawing respectively the bath liquids.The hot water bath compartment may be fitted with a steam inlet forheating the water. The

stabilization bath compartment may also be fitted with an outlet for thesolvent vapors generated its scope, will readily occur to the expert.The

scope of my invention is therefore deemed to be limited by the appendedclaims only.

I claim: 1. A process of manufacturing cellulose nitrates comprisingtreating a cellulose-containing material with a mixed acid comprisingwater-free nitric acid, water-free phosphoric acid and phosphoric acidanhydride.

2. A process'of manufacturing cellulose nitrates An interesting featureof this process is that 7 comprising treating a cellulose-containingmaterial with a mixed acid comprising water-free.

nitric acid, water-tree acetic acid and acetic anhydrlde.

4. A process according to claim 1, wherein said water-tree phosphoricacid anhydride is present in a proportion of between 4% and 10%.

5. A process of manufacturing cellulose nitrates comprising treating thecellulose-containing material with a mixed acid comprising water-freenitric acid and water-tree phosphoric acid and phosphorous pentoxidewhereby the ratio oi nitric acid to phosphoric acid varies between 3:1and 1:100.

6. In the process according to claim 1, the step of stabilizing thenon-pulped nitrated cellulose with a swelling agent.

"I. In the process according to claim 1, the step of stabilizing thepulped ni-trated cellulose with a swelling agent.

8. In the process according toclaim 5, the step of stabilizing theunpulped nitrated cellulose with a swelling agent.

9. In theprocessaccordingtoclaim5,thestep of stabilizing the pulpednitrated cellulose with a swelling agent.

10. A process of manufacturing nitrates of allphatic alcohols comprisingtreating said alcohols with a mixed acid comprising water-tree nitricacid, water-free phosphoric acid and phosphorous pentoxide.

11. A process of manufacturing nitrates oi aliphatic alcohols comprisingtreating said alcohols with a mixed acid comprising water-tree nitricacid, glacial acetic acid and acetic acid anhydride.

vl2. A process of manufacturing nitrates of starch. treating said finelydivided starch with a mixed acid comprising water-free nitric acid,water-tree phosphoric acid and phosphorous 2o pentoxide.

13. A process according to claim 11, the step of stabilizing thenitrated aliphatic alcohol with a swelling, but not dissolving, agent.

' ERNST BERL.

